Contemporary aircraft make extensive use of computer generated displays. Compared to earlier instrumentation, computer generated displays are easier for pilots to use and to understand; an advantage that can prove important when quick decisions must be made. One portion of such a display could be a synthetic view of the ground below the aircraft. Such a view can be generated from raw terrain data such as the commercially available U.S. Geological Survey Digital Elevation Model data or the Defense Mapping Agency's Digital Terrain Elevation Data.
Raw terrain data is stored in a large table. The table stores information about the elevation of each location within the geographic boundaries covered by the table. When an X and a Y coordinate are specified, the system returns an elevation for that particular point from the table. Data points may be, for example, 300 feet apart making a table covering, for example, the United States, extremely large. Such a table would be too large to present in complete detail on a cockpit display. The huge number of data points would simply overwhelm known processors. Even presenting a small section of such a table, such as the data points corresponding to all that is in the field of view of a pilot flying at 10,000 feet could present computational and graphic display difficulties.